Theoretical investigation to characterize the inclusion complex of α-lipoic acid and β-cyclodextrin

We simulated the docking of α-lipoic acid (α-LA) in β-cyclodextrin (β-CD) using two models. We considered in this study complexes formed by 1:1 host–guest stoichiometry in vacuo and in aqueous phase, using PM6, DFT and ONIOM2 hybrid calculations. The results obtained with PM6 method clearly indicate that the complexes formed are energetically favored with or without solvent, model 2 (α-LA entering the cavity of β-CD from its wide side by COOH group) is found more favored than model 1 (α-LA entering into the cavity of β-CD from its wide side by cyclic group), the preference being greater in the case of ONIOM2 calculations. In addition, NBO analysis gives that mutual interactions between the donor and acceptor orbitals of α-lipoic acid and β-CD plays an important role to the stabilization of such a complex. Finally, ¹H nuclear magnetic resonance (NMR) chemical shifts of free and complexed α-LA were calculated by the Gauge-Including Atomic Orbital (GIAO) method and compared with available experimental data. The results of GIAO calculations were analyzed and discussed.